A sclerostomy is a procedure in which the surgeon makes a small opening in the outer covering of the eye-ball to reduce intraocular pressure (IOP) in patients with open-angle glaucoma. It is classified as a type of glaucoma filtering surgery. The name of the surgery comes from the Greek word for "hard," which describes the tough white outer coat of the eyeball, and the Greek word for "cutting" or "incision."
Sclerostomies are usually performed to reduce IOP in open-angle glaucoma patients who have not been helped by less invasive forms of treatment, specifically medications and laser surgery . In some cases—most commonly patients who are rapidly losing their vision or who cannot tolerate glaucoma medications—an ophthalmologist (eye specialist) may recommend a sclerostomy without trying other forms of treatment first.
As of 2003, glaucoma is not considered a single disease but rather a group of diseases characterized by three major characteristics: elevated intraocular pressure (IOP) caused by an overproduction of aqueous humor in the eye or by resistance to the normal outflow of fluid; atrophy of the optic nerve; and a resultant loss of visual field. A sclerostomy works to reduce the IOP by improving the outflow of aqueous humor. Between 80% and 90% of aqueous humor leaves the eye through the trabecular meshwork while the remaining 10–20% passes through the ciliary muscle bundles. A sclerostomy allows the fluid to collect under the conjunctiva, which is the thin membrane lining the eyelids, to form a filtration bleb.
In 1995, the World Health Organization (WHO) reported that over five million people around the world have lost their sight due to complications of glaucoma; about 120,000 Americans are blind as a result of glaucoma. According to the National Eye Institute (NEI), nearly three million people in the United States have the disorder; however, nearly half are unaware that they have it. Primary open-angle glaucoma (POAG) accounts for 60–70% of cases. "Primary" means that the glaucoma is not associated with a tumor, injury to the eye, or other eye disorder.
Although glaucoma can occur at any age, it is most common in adults over 35. One major study reported that less than 1% of the United States population between 60 and 64 suffer from POAG. The rate rises to 1.3% for persons between 70 and 74, however, and rises again to 3% for persons between 80 and 84.
With regard to race, African-Americans are four times as likely to develop glaucoma as Caucasians, and six to eight times more likely to lose their sight to the disease. African Americans also develop glaucoma at earlier ages; while everyone over age 60 is at increased risk for POAG, the risk for African Americans rises sharply after age 40. A 2001 study reported that the rate for Mexican Americans lies between the rate of POAG in African Americans and that in Caucasians. Mexican Americans, however, are more likely to suffer from undiagnosed glaucoma—62% as compared to 50% for other races and ethnic groups in the United States. In addition, the rate of POAG in Mexican Americans was found to rise rapidly after age 65; in the older age groups, it approaches the rates reported for African Americans. Among Caucasians, people of Scandinavian, Irish, or Russian ancestry are at higher risk of glaucoma than people from other ethnic groups.
The question of a sex ratio in open-angle glaucoma is debated. Three studies done in the United States between 1991 and 1996 reported that the male:female ratio for open-angle glaucoma is about 1:1. Three other studies carried out in the United States, Barbados, and the Netherlands, however, found that the male:female ratio was almost 2:1. A 2002 study from western Africa reported a male:female ratio of 2.26:1. It appears that further research is needed in this area.
Most sclerostomies are performed as outpatient procedures under local anesthesia. In some cases the patient may be given an intravenous sedative to help him or her relax before the procedure.
After the patient has been sedated, the surgeon injects a local anesthetic into the area around the eye as well as a medication to prevent eye movement. Using very small instruments with the help of a microscope, the surgeon makes a tiny hole in the sclera as a passageway for aqueous humor. Some surgeons use an erbium YAG laser to create the hole. Most surgeons apply an antimetabolite drug during the procedure to minimize the risk that the new drainage channel will be closed by tissue regrowth. The most common antimetabolites that are used are mitomycin and 5-fluouracil.
After the surgery, the aqueous humor begins to flow through the sclerostomy hole and forms a small blister-like structure on the upper surface of the eye. This structure is known as a bleb or filtration bleb, and is covered by the eyelid. The bleb allows the aqueous humor to leave the eye in a controlled fashion.
A newer technique that was first described in 2002 is enzymatic sclerostomy, which was developed at the Weizmann Institute of Science in Israel. In enzymatic sclerostomy, the surgeon applies an enzyme called collagenase to the eye to increase the release of aqueous humor. The collagenase is applied through an applicator that is attached to the eye with tissue glue for 22–24 hours and then removed. According to the researchers, the procedure reduced the intraocular pressure in all patients immediately following the procedure and in 80% of the subjects at one-year follow-up. None of the patients developed systemic complications. Enzymatic sclerostomy is considered experimental as of mid-2003.
Open-angle glaucoma is not always diagnosed promptly because it is insidious in onset, which means that it develops slowly and gradually. Unlike closed-angle glaucoma, open-angle glaucoma rarely has early symptoms. It is usually diagnosed either in the course of an eye examination or because the patient has noticed that they are having problems with their peripheral vision—that is, they are having trouble seeing objects at the side or out of the corner of the eye. In some cases the patient notices that he or she is missing words while reading; having trouble seeing stairs or other objects at the bottom of the visual field; or having trouble seeing clearly when driving. Other symptoms of open-angle glaucoma may include headaches, seeing haloes around lights, or difficulty adjusting to darkness. It is important to diagnose open-angle glaucoma as soon as possible because the vision that has been already lost cannot be recovered. Although open-angle glaucoma cannot be cured, it can be stabilized and controlled in almost all patients. Because of the importance of catching open-angle glaucoma as early as possible, adults should have their eyes examined every two years at least.
HIGH-RISK GROUPS. Not everyone is at equal risk for glaucoma. People with any of the risk factors listed below should consult their doctor for advice about the frequency of eye checkups:
Some patients should not be treated with filtration surgery. Contraindications for a sclerostomy include cardiovascular disorders and other severe systemic medical problems; eyes that are already blind; or the presence of an intraocular tumor or bleeding in the eye.
DIAGNOSTIC TESTS. Ophthalmologists use the following tests to screen patients for open-angle glaucoma:
Newer diagnostic devices include a laser-scanning microscope known as the Heidelberg retinal tomograph (HRT) and ultrasound biomicroscopy (UBM). UBM has proved to be a useful method of long-term follow-up of sclerostomies.
Preparation for a sclerostomy begins with the patient's decision to undergo incisional surgery rather than continuing to take medications or having repeated laser procedures. Three factors commonly influence the decision: the present extent of the patient's visual loss; the speed of visual deterioration; and the patient's life expectancy.
With regard to the procedure itself, patients may be asked to take oral antibiotic and anti-inflammatory medications for several days prior to surgery.
Patients can use their eyes after filtering surgery, although they should have a friend or relative to drive them home after the procedure. They can go to work the next day, although they will probably notice some blurring of vision in the operated eye for about a month. Patients can carry out their normal activities with the exception of heavy lifting, although they should not drive until their vision has completely cleared. Most ophthalmologists recommend that patients wear their eyeglasses during the day and tape an eye shield over the operated eye at night. They should apply eye drops prescribed by the ophthalmologist to prevent infection, manage pain, and reduce swelling. They should also avoid rubbing, bumping, or getting water into the operated eye. Complete recovery after filtering surgery usually takes about six weeks. Long-term aftercare includes avoiding damage to or infection of the bleb.
It is important for patients recovering from filtering surgery to see their doctor for frequent checkups in the first few weeks following surgery. In most cases the ophthalmologist will check the patient's eye the day after surgery and about once a week for the next several weeks.
The risks of a sclerostomy include the following:
According to the National Eye Institute, sclerostomy is 80–90% effective in lowering intraocular pressure. The success rate is highest in patients who have not had previous eye surgery.
Mortality following a sclerostomy is very low because the majority of procedures are performed under local anesthesia. The most common complications of filtering surgery are cataract formation (30% of patients develop cataracts within five years of a sclerostomy) and closure of the drainage opening requiring additional surgery (10–15% of patients). Bleeding or infection occur in less than 1% of patients.
There are two surgical alternatives to sclerostomy that are called nonpenetrating deep sclerectomies because they do not involve entering the anterior chamber of the eye. The first alternative, viscocanalostomy, is a procedure that involves creating a window in Descemet's membrane (a layer of tissue in the cornea) to allow aqueous humor to leave the anterior chamber; and injecting a viscoelastic substance into Schlemm's canal, which is the main pathway for aqueous humor to leave the eye. The viscoelastic helps to keep the canal from scarring shut following surgery.
The second type of nonpenetrating surgery involves implanting a device called the Aquaflow® collagen wick about 0.8 in (2 cm) long under the sclera. The wick keeps open a space created by the surgeon to allow drainage of the aqueous humor. The wick is made of a material that is absorbed by the body within six to nine months, but the drainage pathway remains open after the wick is absorbed. The Aquaflow wick was approved by the Food and Drug Administration (FDA) in July 2001.
Both types of nonpenetrating deep sclerectomies allow patients to recover faster, with fewer complications than traditional sclerostomies. Their drawbacks include a lower success rate and the need for additional procedures to control the patient's IOP. Viscocanalostomy in particular is not as effective in reducing IOP levels as traditional filtering surgery.
Bilberry (European blueberry) extract has been recommended as improving night vision; it was given to RAF pilots during World War II for this reason. There is evidence that 80–160 mg of bilberry extract taken three times a day does improve night vision temporarily. The plant does not have any serious side effects, but it should not be used in place of regular eye examinations or other treatments for glaucoma.
People who support the medicinal use of marijuana have argued that cannabinoids, the active chemical compounds found in the plant, lower intraocular pressure in patients with glaucoma. According to the Glaucoma Research Foundation, however, very high doses of marijuana are required to produce any significant effect on IOP. A Canadian researcher has concluded that the effects of cannabinoids on IOP "....are not sufficiently strong, long lasting or reliable to provide a valid basis for therapeutic use [of marijuana]."
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American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. http://www.aao.org .
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100.
Canadian Ophthalmological Society (COS). 610-1525 Carling Avenue, Ottawa ON K1Z 8R9. http://www.eyesite.ca .
(The) Glaucoma Foundation. 116 John Street, Suite 1605, New York, NY 10038. (212) 285-0080 or (800) 452-8266. http://www.glaucoma-foundation.org .
Glaucoma Research Foundation. 490 Post Street, Suite 1427, SanFrancisco, CA 94102. (415) 986-3162 or (800) 826-6693. http://www.glaucoma.org .
National Eye Institute. 2020 Vision Place, Bethesda, MD 20892-3655. (301) 496-5248. http://www.nei.nih.gov .
Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (800) 331-2020. http://www.prevent-blindness.org .
Wills Eye Hospital. 840 Walnut Street, Philadelphia, PA 19107. (215) 928-3000. http://www.willseye.org .
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Rebecca Frey, Ph.D.
Sclerostomies are performed by ophthalmologists, who are physicians who have completed four to five years of specialized training following medical school in the medical and surgical treatment of eye disorders. Ophthalmology is one of 24 specialties recognized by the American Board of Medical Specialties.
Sclerostomies are usually done as outpatient procedures, either in the ophthalmologist's office or in an ambulatory surgery center; however, they may also be performed in a hospital with sedation as well as local anesthesia.